New M dwarfs in solar neighborhood

Using the count rate and hardness ratios obtained from the ROSAT catalog, we have derived the X-ray luminosities. Our stars display a "saturation-type" relation between the chromospheric and coronal activity. The relation is such that log(LX/Lbol) remains "saturated" at a value of approximately -3 for varying H{alpha} equivalent width.

We have found 568 matches in the USNO-B catalog and have derived the tangential velocities for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher vtan have lower H{alpha} equivalent widths. The coronal emission, however, remains saturated at a value of log(LX/Lbol)~-3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age.

We do not find any break in the saturation-type relation at the spectral type at which stars become fully convective (~M3.5). Most of the stars in our sample show more coronal emission than the dMe stars in the Hyades and Praesepe and have v_tan_<40km/s, suggesting a young population.